Broly is stronger than the combined strength of 3 Super Saiyans, but weaker than 4. Therefore, SS3 Broly is stronger than 3 SS3s, but weaker than 4. Evil Buu was a bit stronger than SS3 Gotenks. Mystic Gohan was a lot stronger than Evil Buu, but weaker than Buu w/ Gotenks. Super Buu is made of Evil Buu, SS3 Gotenks and Mystic Gohan, meaning he is made of three beings of SS3 strength or higher, but their combined strength is lower than 4 SS3s...

It is evenly matched, so Super Buu should have no difficult absorbing Broly.

And it's impossible to know how strong SS3 Broly is, because LSS isn't a known multiplier, and you can't count in Super Saiyans, because the strength of a Super Saiyan is based on the base power level of the person. SS Goten for example isn't worth as much as SS Goku. We don't actually know how strong base form Broly is, so without that data LSS could be even stronger than SS3 as a transformation and we would never know.

If Goku's power level increases at the same rate till the end of DBGT as it does till the end of the Frieza saga, as a SS4 Goku would have a PL of roughly 939 Quinoctogintillion. For reference that is a 260 digit number. A PL of 14,600 is required to destroy an earth sized planet. There are about 2 nonillion earths worth of mass in the universe. That means SS4 Goku can destroy the universe about 32 Octosexagintillion times over. There's a reason they made Goku a god at the end of GT.